Freeze drying



D. EOLKIN FREEZE DRYING Oct. l2, 1965 Filed March 50, 1962 mn Q m W im m All U/:U x N L F WON- United States Patent O 3,210,861 FREEZE DRYING Dave Eolkin, San Lorenzo, Calif., assignor to Gerber Products Company, Fremont, Mich., a corporation of Michigan Filed Mar. 30, 1962, Ser. No. 183,840 4 Claims. (Cl. 34-5) This invention relates in general to the art of dehydration, and relates more specifically to a process and apparatus for removing large volumes of Water vapor from a dehydration area.

Sublimation of ice directly to the vapor state is a phenomena understood centuries ago. This principle has been used for removal of water from foods at least as early as the beginning of the twentieth century. Freezing followed by vacuum sublimation, and freezing under vacuum conditions to induce sublimation as freezing takes place are two well known varieties of food processing. These processes have been used commercially only in areas Where cost is less a factor than results.

The process has not become commercially acceptable for large scale preservation because of the exceedingly high volume of water vapor gas produced for each pound of water to be removed from the food substance. The sublimation must take place at relatively low pressure to be acceptable, and at low pressures the water produces such a huge volume of vapor that exceedingly expensive pumping apparatus must be employed to carry away the Volume of water vapor. Accordingly, the art has tended to develop along other lines of endeavor.

It is an object of the present invention to change the form and to reduce the volume of the water prior to its removal from the low pressure area.

More specifically, it is an object of this invention to return the vaporized water to a solid state within the low pressure area and then remove the water from the system in the highly condensed solid state.

A further object of the invention is to remove true gases at the pressure of the chamber by means of a gas vacuum pump, and to remove water through a pump designed to handle liquids and slurries.

The objects are broad statements which may possibly apply to processes and apparatus other than this invention. They, nevertheless, outline the course of this invention. It is a further and principal object of this invention to change the water from a vapor state to an amorphous solid state.

Most substances which may be carried to a vapor and back to a solid state are crystalline in the solid state. Energy is required, or is given off, according to the direction of change. It is possible by control of circumstances to solidify from a vapor to an amorphous state or a crystalline state of low-er energy than common ice and without the extraction of the high heat of crystallization found in such common ice. Accordingly, it is one of the principal objects of this invention to condense the water vapor in a shower of low temperature condensing spray and this causes at least a portion of the vapor to solidify.

A still further object of the invention is to cause the solidified water to be intimately mixed with the material of the low temperature shower and form a pumpable conglomeration.

Further, it is the object of the invention to provide apparatus which will carry out the process in an eicient and economical manner.

While the present invention has been described in connection with a particular embodiment, it should be apparent to those skilled in the art that numerous other variations are within the spirit and scope of the present ICC invention. For this reason, the invention should only be limited to the extent of the claims. l

`The single figure of the drawing is a schematic illustration of a preferred complete arrangement of the invention. v

In the drawing, the reference character 10 indicates a drying chamber area which is the source of water vapor to be removed. This invention was created with particular interest in the food and drug art for the sublimation removal of water vapor. However, this invention is in no means restricted to the food or drug industries, and will serve any apparatus giving oif relatively large volumes of Water vapor at low pressures.

An exhaust outlet 11, having condensation chamber 12 therein leads to a vacuum pump 14.

A spray nozzle 15 at the top of chamber 12 permits the introduction of a finely divided mist of material which will fall to the bottom of the chamber by means of gravity. The material is then collected and withdrawn through an outlet 16 by means of a pump 17. In the preferred embodiment of the invention a liquid material is employed and created as spray in the chamber 15 by means of the spray nozzle 15.

Prior to this invention it was necessary to provide complicated systems to handle the exceedingly large volume of water vapor coming from a low pressure dehydration chamber. Continuity of operation was difcult if not impossible to attain because of the need to de-ice the freezer plates. The conventional vacuum pump 14 is considerably smaller than necessary to handle a commercial quantity of water vapor but is quite efficient for removal of all gases other than water vapor which are created in such a chamber.

According to this invention a finely divided spray of cold material is introduced at the top of the chamber 12 and allowed to fall to the bottom of the chamber. 'Thus, the water vapor passing through the chamber 12r is exposed to and mixed with a cold spray of material which is below the freezing temperature of that water vapor under the particular circumstances of vacuum which had been created. Students of natural phenomena are aware of the fact that a high vacuum is created by the changing of the volume of vapor to a much smaller volume of liquid within a closed container. Condensing steam within a can will cause the can to collapse. In this instance, the change of state of the water Vaporpassing through the finely divided carrier material introduced by the nozzle 15 changes state and falls to the bottom of the chamber along with the carrier material. Hence, the condensation of the water vapor is in reality a vacuum pump as Well as being a means of eliminating water vapor and preventing that vapor from going to the vacuum pump which is not designed to carry water vapor.

Furthermore, the carrier material as it falls to the bottom of the chamber will be intimately mixed with the frozen water vapor and will act as the means to assist in carrying the solidified water vapor ice from the chamber through the opening 16 as the pump 17 operates to evacuate such material. Therefore, there is no requirement for mechanical devices to present a surface for the freezing of the water vapor and then scraping and otherwise cleansing such a freeze surface. According to this invention the frozen vapor acts substantially as a liquid and moves with the carrier material by the simple expedient of a pump.

It is a subject of speculation that the extraordinarily simple and efficient pump device in the water removal system thus described may be further enhanced by the ability, under certain circumstances, to cause the water vapor -to condense in an amorphous state and hence change into Va .pumpable condition with a far lower heat transfer requirement. As a general indication, if operating conditions permit the creation of amorphous solidification of the water vapor, up to about a four hundred percent reduction in refrigeration costs are obtainable. About twelve hundred British thermal units (B.t.u. per pound of energy must be removed to transform a pound of water vapor into the crystalline form of ice. Only about three hundred B.t.u are required for the change to Iamorphous ice. Those familiar with the physics of Water systems will understand the control situation needed for the production of amorphous ice, and when it can be applied to a condensation chamber such as the one suggested in the drawing of this disclosure.

The amount of the carrier material to be passed through the chamber and the temperature of the carrier material are variables within the skill of the operator. The material will serve as the only means for extract-ing the energy from the water vapor 4in sufficient quantities and with sufficient speed to cause that vapor to condense before it can pass through the chamber into the vacuum pump. A very small quantity of oil, for example, at exceedingly low temperature, may be entirely insufficient to absorb the heat energy and hence, failure will result. On the other hand, a large volume of oil at moderate temperature might have a theoretical capacity to absorb all of the heat energy, but be 'impractical because the thermal gradient is insufficient.

Again, if the amorphous state of ice is achieved by rigidly controlled conditions of such rapid solidification, then ice crystals do not have time to form. A high thermal gradient is needed to achieve the creation of amorphous ice conditions. The percentage of water vapor that crystallizes as opposed to that portion which can be made into the amorphous state will depend upon the volume of vapor and the extent of the thermal gradient Those skilled in the art will understand and be able to operate the apparatus from this description of the conditions and needs for the system.

The drawing sets forth a preferred arrangement for the invention associated with the commercial food freezing and dehydration system. For such a system a condenser oil serves adequately as the carrier material to spray through the chamber 12. Condenser oils are well known to have low vapor pressure at the temperature of condensation in the chamber. They are not miscible with water and present a very low solubility characteristic to water. They have a low viscosity at condensing temperature and are very stable. Oil and chemical engineers are well qualified to provide and produce vai-.1- ants of condenser oil and other natural and synthetic products suitable for carrying out the necessary steps.

Referring to the drawings, a preferred system is illustrated for carrying out this invention wherein pump 17 is provided in flow communication with the chamber 12 to pump oil and ice conglomeration through outlet 16. The conglomeration is pumped through a vacuum isolation valve 18 to a centrifuge 19. At the centrifuge station 19, the bulk of the clean condensing oil is separated from the water and the oil is then taken off in line 21 by pump 22 to ow into condenser oil heat exchanger 23. During the passage from chamber 12 through centrifuge 19 to heat exchanger 23 for recycling back to chamber 12 through line 24 the condenser oil picks up little or no temperature increase.

The remaining conglomeration of oil and ice consisting of only a minor portion of oil is in a sufficiently uid state as to render it pumpable and it passes from centrifuge 19 through line 31 and pump 32 to the refrigerant cooling heat exchanger 33. At station 33 the ice melts and separation of oil and water occurs with the water being dumped from the system through drain 34. The separated condenser oil is then passed through line 35 to rejoin the major portion of the clean cold condenser oil in line 21 for recycling through heat exchanger 23 for cooling to the proper point before recycling to chamber 12 through line 24 and vacuum isolation valve 25.

The refrigerant system comprises a compressor 41, a cooling tower 42, and line 43 which leads to the coil of heat exchanger 33. A refrigerant line 44 leads from the coil of heat exchanger 33 to a collector or sump 45. A take-off line 46 and the associated expansion valve are connected to .the collector 45 and the coil of heat exchanger 23. A return flow line 47 connects the coil of heat exchanger 23 back to the compressor 41 for recycling and recooling of the refrigerant.

The system thus described enables the water vapor leaving the food processing chamber to be exposed to a spray cloud or fog of condenser oil in chamber 12. The oil is cold and capable of taking enough heat energy from the vapor to cause it to condense as a solid. The water vapor and oil spray form a conglomeration of intimately mixed materials and the temperature is suiicently below freezing temperature of the water vapor to enable the water vapor to substantially change in state, thus creating and maintaining a high degree of vacuum. Under proper operating conditions, the vapor may go to an arnorphous state. There is a vacuum pump provided to take off the non-condensed gaseous material from the system and maintain the vacuum conditions with respect to gases other than water vapor.

The ice and oil fall to the bottom of the chamber 12 where they are intimately mixed but not dissolved in one another. The exceedingly fine nature of the solidified ice from the water vapor enables the material conglomeration at the bottom of the chamber to flow as a pumpable fluid. Separation of the oil and water by means of the centrifuge station results in recovery of a major amount of the oil by mechanical means leaving only a minor part of the oil intermixed with the ice. There is very little heat gain, if any, in the major part of the oil thus recirculated to the refrigerant heat exchanger 23 and recycled to the chamber 13, and thus little energy requirement is made upon the refrigerant system iricluding compressor. The minor quantity of oil separated for further 4processing is subjected to the refrigerant at heat exchanger 33 at which point the water is dumped out and the oil is recirculated to the heat exchanger 23 with resultant small loss in the lower temperature value of the refrigerant material. The amount of oil so treated is relatively small and thus requires a correspondingly small amount of energy from the refrigerant system. The two-stage treatment of the condenser oil enables a balance to be preserved in the systern which contributes to its efficiency over known systems of freeze-out methods of processing.

Further, the accumulation of ice in the normal freezeout system builds up on the plates or other metallic surfaces and requires a larger output of power energy to reduce the operating temperatures necessary to overcome the effects of the accumulated ice. The greatly increased heat transfer ability in the present system which resides in the spray-vapor system will result in a potential use of higher ice-condensing temperatures and a consequent lowering of necessary compressor requirements and energy output.

The refrigeration system and the system employed for rejuvenation of the carrier material are integrated into a novel and useful system which increases the overall efficiency of the present invention to an extraordinary degree. In the preferred arrangement using oil as the carrier, the oil-ice conglomeration must be warmed sufficiently to change the state of the Water for efficient removal of only a minor portion of oil. The major portion has already been removed without reference to the refrigerant system. The diied oil must be cooled below the temperature necessary to condense the ice in the chamber 12. The refrigeration system needs the cooling effect on the high pressure side of the system to become efficient. The two systems, as illustrated, complement one another perfectly and are balanced for the complete operation of the preferred embodiment of this invention in an efficient and economic fashion.

What is claimed:

1. A process for freeze drying for removal of a large volume of water vapor and other gas from a low pressure sublimation dehydration area interconnected with a chamber, liquid carrier heat exchanger and refrigerant heat exchanger, comprising the steps of providing a chamber connected to said dehydration area, evacuating gas other than water vapor from said chamber through a rst outlet to a predetermined low pressure level, providing a liquid carrier material at a temperature at least as low as the solidication temperature of water vapor at said predetermined pressure level, injecting said carrier material into said chamber in a nely divided state, said carrier material from the conglomeration at a rst remain in the state introduced into said chamber at said predetermined pressure level, forming a conglomeration of frozen water vapor ice and carrier material, pumping the said conglomeration from said chamber through a second outlet, mechanically separating a major portion of said carrier material from the conglomeration at a first separation station, maintaining said carrier material at a substantially constant temperature and said water vapor ice in a frozen condition during the mechanical separation, flowing said major portion of carrier material to said liquid carrier heat exchanger, separating a remaining minor portion of carrier material from the frozen water vapor ice at a second separation station by owing the remaining minor portion of carrier material and said water vapor ice to said refrigerant heat exchanger, and collecting and returning said minor portion of carrier material to said major portion of carrier material.

2. The process of claim 1 in which the step of mechanically separating includes centrifugally separating a major portion of the carrier material from a minor portion of the carrier material and frozen Water vapor ice.

3. In low pressure freeze drying apparatus of the type having a water vapor chamber maintained at low pressure and means for passing a nely divided spray mist of a liquid carrier material therethrough, the carrier material being below the freezing temperature of water vapor in said chamber to form a conglomeration comprising carrier material and frozen water vapor ice, and including a rst heat exchanger separating means in fluid flow communication with said vapor chamber for receiving and warming said conglomeration above the melting temperature of ice, and a Second liquid carrier heat exchanger for receiving and cooling liquid carrier material, the improvement comprising the combination therewith of mechanical means linked between said vapor chamber and said separating means for removing a major portion of said carrier material from the conglomeration at a temperature substantially equal to that of the carrier material when first entering said mechanical means, rst propelling means owing said major portion into said second heat exchanger, said rst heat exchanger interconnected to said mechanical means, and receiving from said mechanical means a minor portion of said carrier and frozen water vapor ice, means to withdraw water from said first heat exchanger, and a second propelling means combining said minor portion of said liquid carrier material with said major portion.

4. The improvement in accordance with claim 3 Wherein said mechanical means comprises a centrifuge.

References Cited by the Examiner UNITED STATES PATENTS 2,507,632 5/50 Hickman 34-75 2,613,513 10/52 Shields 34-75 2,657,555 11/53 Wenzelberger 62-58 2,663,089 12/53 Coats 34-75 2,746,168 5/56 Rickabaugh 34-75 2,913,883 11/59 Burgess 34-75 2,933,826 4/60 Justus 34-75 FOREIGN PATENTS 46,243 7/ 39 Netherlands.

NORMAN YUDKOFF, Primary Examiner. 

1. A PROCESS FOR FREEZE DRYING FOR REMOVAL OF A LARGE VOLUME OF WATER VAPOR AND OTHER GAS FROM A LOW PRESSURE SUBLIMATION DEHYDRATION AREA INTERCONNECTED WITH A CHAMBER, LIQUID CARRIER HEAT EXCHANGER AND REFRIGERANT HEAT EXCHANGER, COMPRISING THE STEPS OF PROVIDING A CHAMBER CONNECTED TO SAID DEHYDRATION AREA, EVACUATING GAS OTHER THAN WATER VAPOR FROM SAID CHAMBER THROUGH A FIRST OUTLET TO A PREDETERMINED LOW PRESSURE LEVEL, PROVIDING A LIQUID CARRIER MATERIAL AT A TEMPERATURE AT LEAST AS LOW AS THE SOLIDIFICATION TEMPERATURE OF WATER VAPOR AT SAID PREDETERMINED PRESSURE LEVEL, INJECTING SAID CARRIER MATERIAL INTO SAID CHAMBER IN A FINELY DIVIDED STATE, SAID CARRIER MATERIAL FROM THE CONGLOMERATION AT A FIRST REMAIN IN THE STATE INTRODUCED INTO SAID CHAMBER AT SAID PREDETERMINED PRESSURE LEVEL, FORMING A CONGLOMERATION OF FROZEN WATEWR VAPOR ICE AND CARRIER MATERIAL, PUMPING THE SAID CONGLOMERATION FROM SAID CHAMBER THROUGH A SECOND OUTLET, MECHANICALLY SEPARATING A MAJOR PORTION OF SAID CARRIER MATERIAL FROM THE CONGLOMERATION AT A FIRST SEPARATION STATION, MAINTAINING SAID CARRIER MATERIAL AT A SUBSTANTIA6LY CONSTANT TEMPERATURE AND SAID WATER VAPOR ICE IN A FROZEN CONDITION DURING THE MECHANICAL SEPARATION, FLOWING SAID MAJOR PORTION OF CARRIER MATERIAL TO SAID LIQUID CARRIER HEAT EXCHANGER, SEPARATING A REMAINING MINOR PORTION OF CARRIER MATERIAL FROM THE FROZEN WATER VAPOR ICE AT A SECOND SEPARATION STATION BY FLOWING THE REMAINING MINOR PORTION OF CARRIER MATERIAL AND SAID WATER VAPOR ICE TO SAID REFRIGERANT HEAT EXCHANGER, AND COLLECTING AND RETURNING SAID MINOR PORTION OF CARRIER MATERIAL TO SAID MAJOR PORTION OF CARRIER MATERIAL. 